This relates to digital screen displays and more particularly to touch screen displays.
Touch screen technology refers to the ability of a screen device to detect and position fix when and where a finger, or some other element, makes contact with the screen. Such technology is growing in popularity and may be found in an increasing number of applications, including various types of displays that appear as monitors/televisions in homes, offices, and vehicles. One type of display is the rear projection display, which is characterized by some type of projecting device that is located behind the screen, that is, on the opposite side of the screen from the side that is viewed by a user. Newer rear projecting devices implement differing technologies to modulate the image that is displayed, including DLP® technology from Texas Instruments Incorporated.
Various conventional approaches have been implemented to attempt touch screen detection in rear projection devices, although such approaches also may have limitations.
One conventional approach to rear projection touch screen technology is to include one or more infrared (IR), or near-IR, elements, and a camera, inside the projector (i.e., on the non-viewer side of) and at positions away from the screen. In operation, each IR or near-IR element emits its respective light toward and through the rear side of the screen so that, desirably, as a finger or other object touches the front of the screen, the finger/object is illuminated by the IR/near-IR light and the camera captures the reflection of the IR/near-IR light from the finger/object. Next, photo-imaging circuitry processes the camera-captured data and attempts to discern the reflection captured by the camera and associate a screen position with the reflection as corresponding to a screen touch. While this approach has some level of accuracy in detecting screen touches, it also is vulnerable to errors due to apparatus that are often included in the path of the IR/near-IR light. More particularly, displays usually include one or more light directing layers or apparatus, for purposes of directing the internally-projected light image accurately and aesthetically to a viewer of the screen. For example, a Fresnel lens is commonly included, which accepts rear projected light and attempts to normalize it all to a direction perpendicular to the screen. As another example, a diffuser is also commonly included, which receives the normalized light from the Fresnel lens and then diffuses some of it off the axis from which it was received, so as to allow some viewers to see an acceptable image quality from an axis other than directly in front of the screen. As a final example, the display may include other light affecting apparatus/layers, including one to reduce glare or reject ambient light that exists on the viewer's side of the screen. However, recalling that the touch detection is enabled by IR/near-IR emitters inside the projector, any one or more of these layers/apparatus may affect the light as it passes from the emitter, toward such layers/apparatus, in an effort to reach a finger/object as it approaches or touches the viewer side of the screen. Specifically, such layers/apparatus may cause additional reflections, thereby creating non-uniformity reflections or so-called “hot spots” that are captured by the IR/near-IR sensing camera. These captured non-uniformities may be wrongfully interpreted as screen touches or may require extensive additional signal processing so as to distinguish from actual screen touches.
Another conventional approach to rear projection touch screen technology again uses a camera inside the projector, along with an IR, or near-IR, illuminator adjacent the outside/viewer side of the screen. The light from the illuminator is passed through a lens (usually cylindrical) that thereby projects the light in a “curtain” or “fan” across a majority or all of the viewer's side of the screen. An interactive touch thus interrupts the light curtain, thereby causing reflections, and the camera and processing technology is akin to that described above, so as to attempt to detect a reflection and its position relative to the screen area. This approach also has some level of accuracy in detecting screen touches, but likewise has drawbacks. For example, some modern and anticipated displays include curvatures or other interruptions or departures from the traditional planar surface—the single illuminated curtain is not feasible for such structures.
Still another conventional approach to rear projection touch screen technology again uses a camera inside the projector, and in this instance the IR/near-IR light is applied or injected to an edge of the screen, which may be an acrylic material. This approach requires the maintenance of total internal reflection (TIR), in which the refractivity of the screen material and air have a certain ratio so that, when undisturbed, the edge-injected light reflects solely within the screen material. When a touch occurs at the screen, however, this frustrates the TIR, thereby permitting light reflections that were formerly maintained within the screen material to release, and that release may be detected by the related camera. This approach also has some level of accuracy in detecting screen touches, but likewise has drawbacks. For example, various restraints and considerations are required to maintain the TIR. As another example, as was the case with the light curtain approach, the introduction of screen curvature causes difficulty if not an impossibility of implementing this approach, as such curvatures may eliminate the ability to maintain an adequate TIR.